Method of introducing hard phases into metallic matrices



Mmh zo, 1962 METHOD OF' INTRODUCING HARD PHASES INTO METALLIC MATRICESE. GREGORY 3,026,200

Filed Oct. 11, 1956 IVENTOR .5R/f @eww/PY ATTORN EYSv .sr/e555 (LONG'roms/SQ. f/v.)

3,026,260 MEM-lill) F liN'lRUDUClNG HARD PHASES ENT@ METALLIC MATRICESEric Gregory, Hastings on Hudson, N.Y., assigner to 134 WoodworthCorporation, a corporation of New Yorlr Filed Oct. ll, 1956, Ser. No.@5,335 6 Claims. (Cl. 75-224) The present invention relates to theproduction of a reinforced metal product and, more particularly, to amethod of introducing a hard refractory oxide phase into a ductile'metalmatrix. i'

lt is known that high temperature strength properties of certain ductilemetals can be improved by the addition to the metals of a discrete hardphase, e.g. A1203, which increases the metals resistance to deformationand enables it to sustain high stress at elevated temperatures forprolonged periods of time. Wrought aluminum products produced from finealuminum powders exhibit such improved properties in comparison toaluminum products made by conventional casting. This is because aluminumpowders are generally characterized by a surface oxide coating whichremains in the final product as finely dispersed hard particles ofA1203. These particles behave as slip inhibitors and it is largely thischaracteristic that stiffens the metal or alloy and raises itsresistance to applied stress at elevated temperatures. The disperse hardphase acts as a deterrent to recrystallization and grain growth and thusinhibits or decreases the metals tendency to weaken and soften atelevated temperatures.

There have been recent trends to employ this disperse phase hardeningmechanism in stifrening heat resistant alloys, for example an alloycontaining 80% nickel and 20% chromium. A given amount of hard phase,e.g. titanium carbide powder, is added to the foregoing type alloy inthe powder form and the two mechanically mixed to obtain a uniformdistribution of one in the other. The mixture is consolidated into acompact and then hot worked at an elevated temperature into a desiredshape. The fine dispersion of the carbide stiffens the matrix of thealloy and confers additional resistance to deformation at high stressesat elevated temperatures. In order to obtain full benefit, the hardphase must be substantially insoluble in the matrix of the alloy,otherwise the alloy will lose its stiffness and soften due to thesolution of the hard phase in the matrix metal.

One of the disadvantages of the foregoing method of introducing hardphases into the matrix was the tendency for mechanically mixed materialsto segregate. Because of this effect, it was not always consistentlypossible to maintain a perfect mixture. Even when the powders wereblended under the best possible mixing conditions, there was still theproblem of segregation during storage, handling, processing, pressing,etc. If the powders were stored for any length of time and subjectedinadvertently to extraneous vibration usually prevailing in buildingsmaintaining large presses, reciprocating vacuum pumps, and other heavyindustrial machines and equipment, the powders would tend to segregatedue to marked differences in densities and, unless the powders wereremixed, the final product would be affected due to nonuniformdistribution of the slip-inhibiting phase in the nal product.

The present invention overcomes the foregoing dil-liculties by providinga method for insuring uniformity of the final product by enabling theproduction of a metal powder in which substantially each particlecontains a slip-inhibiting phase associated with it as a disperse phase.

It is, therefore, an object of the present invention to provide a methodof introducing a hard disperse phase into hired braten lfatent 3,025,200Patented Mar. 20, 'i962 a ductile metal powder prior to consolidatingthe powder into a solid shape, thereby insuring a uniform distributionof said hard phase throughout the final product.

These and other objects will more clearly appear from 5 the followingdescription when taken in conjunction with the drawing in which FIG. 1depicts curves comparing the physical properties of an internallyoxidized material, the same material not oxidized, and straight copper.

The introduction of the hard phase is achieved by i11- ternallyoxidizing a ductile matrix metal powder having alloyed therewith arefractory oxide-forming metal whose oxide is substantially stable atelevated temperatures. By the term internally oxidizing is meant theintroduction of oxygen through diffusion into and through the powderparticle structure from the surrounding atmosphere during the specialheat treatment. The matrix metal should be relatively noble compared tothe refractory oxideforming metal contained therein. Examples of suchmetals for the purposes of this invention are silver, `gold, copper,platinum, palladium, nickel, cobalt, iron, and alloys based on one ormore of these metals, etc. Such metals may be selected broadly from thecopper group, platinum group, and iron group metals.

Examples of refractory oxide-forming metals include silicon, aluminum,magnesium, beryllium, zirconium, titanium, thorium, rare earth metalssuch as cerium, lanthanum, neodymium, etc., and similar metals whichcombine chemically with oxygen to form hard, refractory oxides havingmelting points of about l500 C. and above.

The so-called ductile metals are also defined broadly as those metalshaving a melting point of at least about 750 C. and whose oxides have anegative free energy of formation at 25 C. below 70,000 calories pergram atom of oxygen. For the purposes of this invention, the refractoryoxide-forming metal has a negative free energy of formation with oxygenof over 90,000 calories per gram atom of oxygen, and generally over120,000.

The following table compares approximate values of free energies offormation of some noble metal oxides with sorne refractory oxides at 25C.:

Noble Metal Oxide AF 1 Refractory Oxide 1 Free energy of formation incalories per gram atom of oxygen.

2 Buttle.

3 Alpha alumina.

4 Heat of formation. Free energy is a little lower than this value.

Platinum oxide has a negative free energy of formation below 20,000calories per gram atom while the value for palladium oxide is below17,000 calories.

Since the amount of the refractory oxide-forming metal alloyed with themore noble matrix metal is usually small, for example in amounts of upto about 5% by weight, generally from about 0.05 to 2.5%, the matrixmetal is also prone to oxidize during the oxidizing treatment. Dependingupon composition, temperature and oxygen partial pressure, therefractory oxide will form within the alloy powder particle in the formof fine particles. In addition, the powder particles may be covered by asurface scale oxide of the more noble matrix metal, provided the matrixmetal oxide is stable. Generalizing in the case of silver, the oxideAg2O is relatively unstable because of its rather low negative freeenergy of formation, while in the case of iron, the oxide Fe2O3 iscomparatively more stable because of its higher negative free energy.

If the matrix metal oxide is allowed to remain on the surface of thepowder after the oxidation treatment, and the powder then used to formsolid shapes by powder metallurgical techniques, the resulting productwill not exhibit the results desired at elevated temperatures as thematrix metal oxide is relatively unstable at elevated temperatures, hasa higher solubility in the matrix metal at such temperatures and isprone to react with stronger oxide formers contained therein. Therefore,it is important that the formation of matrix metal oxide either beinhibited or, if it forms, removed by a subsequent operation prior toforming solid shapes from the treated powder.

The conditions `for the formation of a stable dispersion of refractoryoxide compound R in a more noble metal -N or, by diffusing element Ointo solid solution N and R are as follows:

(1) O must diffuse more rapidly in the more noble metal solvent Nthansolute R does, otherwise a surface layer RO will be formed.

(2) The free energy of formation of the compound RO must be much morenegative than that of compound NO.

When-gases are soluble in metals, they generally diffuse far morequickly than do metallic solute elements and, therefore, they areideally suited to the formation of a dispersed phase by this method. Ingeneral noble metals, e.g. silver, alloyed with a small percentage of ametal having a high ainity for oxygen, e.g. aluminum, are very suitablefor internal oxidation.

A large difference between the free energy of formation of the oxide ofthe solute and the oxide of the solvent favors the formation of smallparticles. Thus, the particles formed von the oxidation ofsilver-aluminum alloys are far smaller than those obtained insilver-silicon, which, in turn, are smaller than those formed in`copper-silicon alloys under the same conditions.

The particle size is affected by the rate of diffusion of the solutemetal outwards relative to that of the oxygen inwards. When the tworates are equal either an external scale or a continuous inner oxidefilm is formed and when the oxygen diffuses only slightly faster thanthe solute the resulting particles are large. Factors which alter thedifference between these diffusion rates will change the size of theparticles and the tendency to form continuous films.

For silver alloys it was found that increasing the temperature ofoxidation, other factors being constant, increases the average particlesize and the tendency to form inner oxide films. Increasing theconcentration of the solute has a Similar effect.

The importance of some of the above lvariables were shown by preliminaryexperiments on a wire specimen of silver alloy containing 0.13% silicon.This was vacuum annealed at 900 C. to obtain a large stable grain sizeand the specimens were heated in air at 650 C., 750 C. and 850 C.Oxidation at 650 C. led to the production of a dispersed phasethroughout but at 850 C. an inner oxide film was formed very close tothe surface. When the oxidation was carried out at 750 C. the inneroxide film was still present and in this case close to the center of thewire. Material which had been vacuum annealed at 675 C. and had a finegrain size could not be oxidized throughout at 650 C. in air owing tothe formation of an inner oxide iilm. This may have been due to thefaster diffusion of silicon along the grain boundaries compared withbulk diffusion through the grains. Fine grained material having a muchgreater grain boundary area than the coarse grained, will allow thesilicon to diffuse outwards more quickly and favor the formation ofcontinuous films.

Increasing the oxygen partial pressure over silver alloys increasestheconcentration gradient of oxygen, decreases the particle size of thedisperse hard phase, andreduces the probability of forming continuousfilms, the ne grained and coarse grained materials were both oxidizedthroughout at all temperatures between 675 C. and 850 C. by heating inoxygen.

A complete explanation of such effects must take into account theoverall rate of movement of the oxidation front and how this isinfluenced by changes in (a) the oxygenrrate of penetration with depthand (b) the rate of migration of aluminum as influenced by changes inconcentration gradient as oxidation occurs.

The oxidation of massive metal, such as a wire of a copper alloycontaining small mounts of solute aluminum, had its limitations inimproving the physical properties of the alloy wire. It was not alwayspossible to obtain adequate internal dispersion of hard phase, eg.A1203. This was true in instances where the alloy had a high aluminumconcentration gradient relative to that of oxygen as might prevail in acopper alloy containing about 1% aluminum. Such an alloy oxidized inair, other conditions being equal, was more prone to form an internaloxide -iilm below the metal surface comprising substantially A1203.which inhibited further diffusion of oxygen into the interior of themetal wire which usually gave rise to large areas deficient in dispersehard phase. Because of this, the full benefits of the hard phase-formingelement could not be utilized adequately and thus there was a limit asto the amount of solute metal that could be tolerated in a particularsolvent metal.

The present invention overcomes the foregoing diiiculty by .usinginternally oxidized, finely divided powder as the starting material (forexample, particle size preferably below 300 microns, and more preferablybelow microns). As long as there is some internal oxidation, the finalproduct resulting from the treated nely divided powder will havegenerally a more uniform dispersion of hard phase throughout its crosssection than in the case of an internally oxidized wire. An importantfeature of using metal powders is that more of the solute phaselformingmetal can be tolerated in the alloy powder than in massive metal, andthus greater benefits property-wise can be realized.

As illustrative of the invention, the following examples are given:

Example I A finely divided alloy powder (minus 300 microns) containing0.5% aluminum and the balance copper was internally oxidized in air at atemperature of about 1000 C. for a few minutes (below ten minutes). Theoxidized powder had a surface scale enriched in copper oxide and a smallamount of internal oxidation. The material was then heated in an inertatmosphere of nitrogen at 900 C. for about one hour. During lthisheating the surface oxide decomposed and acted as a source of oxygenwhich diffused into the powder particles to form A1203 with thealuminum, most of the surface oxide being reduced to pure copper. Somecopper oxide remained on the surface and this was reduced by heating thepowder to 600 C. in an atmosphere of hydrogen. The powder was then coldcompacted in a confining die at a pressure of about 30 tons per squareinch, thereafter heated to 900 C., placed in a cold die mold, and apressure of 30 tons per square inch applied immediately. The billet thusformed was hot extruded at a temperature of about 900 C. at an extrusionratio of about 20 to 1 under a pressure of about 50 tons per squareinch. The stress rupture and creep properties were obtained and comparedto similar properties obtained for pure copper (note PIG. l).

FIG. 1 shows the relationship between creep rate and stress for theinternally oxidized material (l), the same material in the unoxidizedcondition (2), and material made from straight copper powder (3).

The internally oxidized material (l) comprising I0.5% aluminumand thebalance copper was produced in accordance with Example I. The unoxidizedmaterial (2) was produced from the same powder lot as (1) except theoxidation step was omitted while (3) was produced from straightelectrolytic copper powder. All three powders were fabricated similarlyinto solid shapes. It will be seen that at low stresses the internallyoxidized material has considerably improved creep resistance over thosef the other two materials. Also it is significant that the latter [(2)and (3)] show instability breaks associated with recrystallization. Thisis absent in results of the internally oxidized material (l), showingthe stability resulting from the presence of the finely dispersed phase.

Example ll A finely divided alloy powder (minus 300 microns) containing0.5% silicon and the balance copper was internally oxidized in air at atemperature of about 925 C. for about one hour. yThe oxidized powder hada surface scale enriched in copper oxide and a small amount of internaloxidation. The material was then heated in an inert atmosphere ofnitrogen at 925 C. for two hours. During this heating, the surface oxidedecomposed and acted as a source of oxygen which diffused into thepowder particles to form SiO2 with the silicon, most of the surfaceoxide being reduced to pure copper. Some copper oxide remained ou thesurface and this was reduced by heating the powder to 750 C. in anatmosphere of hydrogen for about five minutes. The powder was then coldpressed in a confining die at a pressure of about 40 tons per squareinch, thereafter heated to 900 C., placed in a cold die mold and apressure of 40 tons per square inch applied immediately. The resultingcompact was then hot extruded at a temperature of labout 900 C. at anextrusion ratio of about 20:1 under a pressure of about 50 tons persquare inch. The extruded material had a yield strength of about 19,700p.s.i. as compared to a similarly extruded material of electrolyticcopper powder which exhibited `a lower yield stress of 12,600 p.s.i.

A finely divided powder comprising 1% zirconium and the balnace nickelmay be similarly treated by subjecting said powder (eg. minus 150microns) to oxidation in air" at 950 C. for about one hour followed byheating for several hours at 1000 C. in a nitrogen atmosphere to promotethe internal oxidation of the powder via the decomposition of the nickeloxide forming the surface scale. A substantial amount of the containedzirconium is thus converted to fine particles of ZrO2. The powder isthereafter subjected to the reducing action of hydrogen, or otherreducing gas, to remove the last traces of nickel. oxide from thesurface, after which the resulting internally oxidized powder iscompacted as in Examples I and ll and hot extruded into a desired shape.

Where a nickel-chromium alloy is desired hardened by Zr02, eig. 80%nickel and 20% chromium, the chromium is not 'added until the ZrO2 hasbeen formed otherwise the presence of the large amount of chromium wouldinterfere with the internal oxidation mechanism. First, an intei-nallyoxidized powder of Ni-Zr (eg. 1% zirconium) would be produced asdescribed above and the powder then mixed with powdered chromium,compacted, subjected to an alloying heat treatment and then hot shaped,e.g. by extrusion to the desired configuration.

The present invention is also applicable to the grain stabilization ofplatinum and platinum alloys or metals of the platinum group such asiridium, osmium, palladium, rhodium and ruthenium and to alloys in whichat least one of these metals forms the principal ingredient. Such metalsstabilized by the present invention enable their use at elevatedtemperatures as furnace heating elements, etc. Such refractory oxideformers as thorium (to form thoria), silicon (to form silica), aluminum(to form alumina), etc., may be added in amounts up to 5%, pref erablyfrom 0.05% to 2.5%.

in producing platinum stabilized with thoria, `an alloy powder ofplatinum and thorium of about minus 150 microns is first producedcontaining for example, about 0.75% thoria. The powder is firstsubjected to internal oxidation in air at about 800 C. for about half anhour. Since platinum like silver is relatively stable and does notoxidize to any great extent it need not be subjected to a reducingtreatment but may be directly compacted into a slug and thereafter hotextruded into the desired shape.

It is apparent from the foregoing that a method of introducing a hardphase into a matrix metal is provided comprising starting with a powderof said matrix metal having alloyed therewith a small amount ofrefractory oxide-forming metal having a greater oxide-forming propensitythan the more noble matrix metal, subjecting said powder to internaloxidation by heating at an elevated temperature below the melting pointof said noble matrix metal under oxidizing conditions and then hotforming said oxidized powder to produce a solid shape of said ductilematrix metal having dispersed therethrough tine particles of a hardre'actory oxide. Where part of theV matrix metal is oxidized along withpart of the refractory oxide-forming metal to form some disperserefractory oxide phase and a surface scale of matrix metal oxide, thepowder is additionally treated after the oxidation step by heating it toan elevated temperature, e.g. 900 C., under inert conditions, e.g. in anatmosphere of nitrogen gas, for a time sufficient for the surface oxideto decompose and provide oxygen for diffusion into the underlying metalto form said refractory oxide by reaction with the contained refractoryoxide-forming metal. The excess matrix metal oxide remaining at thesurface is then reduced by heating in `a reducing atmosphere (eg.hydrogen) at an elevated temperature, thereby resulting in a metalpowder having a reduced metal surface but containing internally thereofiinely dispersed refractory oxide.

The invention also provides a novel method for the production of asusbtantially ductile metal powder having dispersed therethrough fineparticles of a refractory oxide, eg. selected from the group consistingof SiO2, A1203, MgO, BeO, ZrCz, TiO2, ThO2, and rare earth metal oxides.

The invention further provides as a composition of matter asubstantially ductile relatively noble metal powder having dispersedtherethrough tine particels of a hard refractory oxide of melting pointabove 1500 C., such as defined above, wherein the ratio of therelatively noble metal to the refractory oxide-forming metalsubstantially combined as the oxide is preferably at least about 19 to land higher.

While the ductile copper group, iron group and platinum group metalshave been given as examples of matrix metals that can be dispersionhardened by the novel process of the invention, it will be appreciatedthat alloysl based on these metals can be similarly treated.

Examples of copper group `alloys are: copper and 5% zinc; 90% copper and10% zinc; 60% copper and 40% zinc; 71% copper, 28% zinc and 1% tin; 65%copper, 17% zinc and 18% nickel; 90% silver and 10% copper; up to 15%nickel and the balance silver; 70% gold and the balance palladium; 69%gold, 25% silver and 6% platinum, etc. These alloys as powderscontaining up to 5% by Weight of refractory oxide formers can beinternally oxidized at temperatures ranging from about 500 C. to 1000C., in an atmosphere at least oxidizing to the refractory oxide former.

Examples of iron group alloys include: certain steels; 64% iron and 36%nickel; 31% nickel, 4 to 6% cobalt, and the balance iron; 54% iron and46% nickel; 99% nickel land the balance cobalt; 68% nickel and 32%copper, etc.

Heat resisting alloys based on the iron group metals may 'also betreated providing such alloying agents as chromium are not added untilthe iron group metal powder containing the refractory oxide-formingmetal has been internally oxidized.

The foregoing iron group alloys as powders containing preferably up toabout 5% by weight of refractory oxide formers may be internallyoxidized at a temperature of about 500 C. to l300 C. in an atmosphereoxidizing to the refractory oxide former. Such an atmosphere couldcomprise oxygen, air or other oxygen containing gaseous media.

Examples of platinum group alloys are as follows: platinum-rhodiumalloys containing up to 50% rhodium; platinum-iridium alloys containingup to 30% iridium; platinum-nickel containing up to 6 or 10% nickel;platinum-palladium-ruthenium containing 77% to 10% platinum, 13 to 88%palladium, and 10 to 2% ruthenium; alloys of palladium-rutheniumcontaining up to 8% ruthenium; 60% palladium and 40% silver, etc. Thesealloys with refractory oxide-forming metal would be treated similarly asthe copper group alloys.

Generally speaking, the oxidizing temperatures must be at least sufcientto oxidize the refractory oxide-forming metal. Such temperatures willrange from 500 C. and up, preferably 600 C. and up.

An important advantage of the invention is that it provides a methodlfor producing a sinterable, internally oxidized powder.

The composite powder produced in accordance with the invention is firstconsolidated before it is hot worked or extruded. `*It is preferred thatthe mixture be consolidated to an apparent density of at least about65%, preferably as near as 90% as possible, before it is hot worked.While in general it would be preferred that the mixture be cold pressed,it will be appreciated that hot pressing can also be employed. Inproducing a compact of at least 65% apparent density by cold pressing,the pressure applied may range from 15 to 50 tons per square inch. Whenhot pressing is employed, the temperature will usually range from about650 C. to 1250 C. at pressures ranging up to about 40 tons per squareinch, lower pressures being employed at higher temperature levels. Wherehigh compacting pressure in conjunction with high temperature isemployed the billet is heated separately, placed in a cold die andimmediately hot compacted. When hot pressing is conducted, it should becarried out under protective conditions, e.g. in a reducing atmosphere,an inert atmosphere or even at subatmospheric pressure.

Likewise, when the compact is extruded, the conditions also should beprotective to the materials forming the compact. Encasing the compact inan air tight, evacuated, welded container, for example a sheath of ironor nickel, is one method of protecting the materials in the compact fromoxidation, etc. Depending on the situation, extrusion pressure may rangefrom about 40 to 250 tons per square inch over a temperature range ofabout 800 to 1250 C. for extrusion ratios ranging from about 14 to l and20 to 1.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

I claim:

l. A method of introducing a hard slip inhibiting phase into asubstantially ductile, matrix metal of melting point above 750 C., anoxide of which has a negative free energy of formation at 25 C. below70,000 calories per gram atom of oxygen, which comprises providing apowder of said matrix metal of minus 300 microns in size having alloyedtherewith up to about by weight of a refractory oxide-forming metalselected from the group consisting of Si, Al, Mg, Be, Zr, Ti, Th andrare earth metals each of whose oxides is substantially stable atelevated temperatures and is characterized by a negative free energy offormation at 25 C. of over 90,000 calories per gram atom of oxygen andhas a melting point over about 1500" C., subjecting said powder tooxidation by heating it at an elevated temperature at least about 500 C.but below the melting point of said matrix metal in an oxidizingatmosphere subjecting said oxidized powder to additional heating in aninert atmosphere at an elevated temperature at least about 500 C. todecompose matrix metal surface oxide and provide additional oxygen fordiffusion into the powder to convert further refractory oxide-formingmetal into disperse oxide phase, heating said treated powder to anelevated temperature below the melting point of the metal powder in areducing atmosphere to reduce excess matrix metal oxide remaining on`the surface of the powder, consolidating said reduced powder to asubstantially solid compact and hot extruding said compact to a desiredshape, whereby said shape is characterized by a uniform dispersionthroughout of fine particles of a hard refractory oxide.

2. A method of introducing a hard slip inhibiting phase into asubstantially ductile, matrix metal powder of melting point above 750C., an oxide of which has a negative free energy of formation at 25 C.below 70,000 calories per gram atom of oxygen, which comprises providingsaid metal powder of minus 300 microns size having alloyed therewith upto about 5% by weight of a refractory oxide-forming metal selected fromthe group consisting of Si, A1, Mg, Be, Zr, Ti, Th and rare earth metalseach of whose oxides is substantially stable at elevated temperaturesand is characterized by a negative free energy of formation at 25 C. ofover 90,000 calories per gram atom of oxygen, subjecting said powder tooxidation by heating it at an elevated temperature at least about 500 C.but below the melting point of said matrix metal in an oxidizingatmosphere subjecting said oxidized powder to additional heating in aninert atmosphere at an elevated temperature at least about 500 C. todecompose matrix metal surface oxide and provide additional oxygen fordiffusion into the powder to convert further refractory oxide-formingmetal into disperse oxide phase, heating said treated powder to anyelevated temperature below the melting point of the metal powder toreduce excess matrix metal oxide remaining on the surface of the powder,whereby a substantially ductile metal powder is produced characterizedby a dispersion throughout of tine particles of a hard refractory oxide.

3. The method of claim 2 wherein the refractory oxideforming metal isemployed in amounts ranging from about 0.05% to 2.5% by weight of thealloy composition.

4. A method of introducing a hard slip inhibiting phase into asubstantially ductile, matrix metal of melting point above 750 C. anoxide of which has a negative free energy of formation at 25 C. of belowabout 7 0,000 calories per gram atom of oxygen, which comprisesproviding a powder of said matrix metal of minus 300 microns in sizehaving alloyed therewith up to about 5% by weight of a refractoryoxide-forming metal whose oxide is substantially stable at elevatedtemperatures and is characterized by a negative free energy of formationat 25 C. of over 90,000 calories per gram atom of oxygen and has amelting point of over about l500 C., subjecting said powder to oxidationby heating it at an elevated temperature but below the melting point ofsaid matrix metal in an oxidizing atmosphere to form a matrix metaloxide coating thereon, subjecting said oxidized powder to additionalheating in an inert atmosphere at an elevated temperature suflicient todecompose said matrix metal surface oxide and provide oxygen fordiffusion into the powder to form a disperse refractory oxide phase withsaid contained refractory oxide-forming metal, heating said treatedpowder at an elevated temperature below the melting point of the metalpowder in a reducing atmosphere to reduce excess matrix metal oxideremaining on the surface of the powder, whereby a substantially ductilemetal powder is produced characterized by a dispersion throughout ofline particles of a hard refractory oxide.

aoaaeoo References Cited in the le of this patent UNITED STATES PATENTSVon Bolton July 13, 1909 Conway Nov. 30, 1937 10 Sachse July 23, 1946Sturnbock Oct. 25, 1949 Hensel et al Dec. 6, 1949 Stern et a1 Oct. 27,1953 Stern et al Oct. 27, 1953 Trifeman July 7, 1959 FOREIGN PATENTSAustralia July 17, 1952 Great Britain June 1, 1955 OTHER REFERENCESMartin et al.: Journal of the Inst. of Metals, vol. 23 (1955), pp.417-420.

1. A METHOD OF INTRODUCING A HARD SLIP INHIBITING PHASE INTO ASUBSTANTIALLY DUCTILE, MATRIX METAL OF MELTING POINT ABOVE 75O*C, ANOXIDE OF WHICH HAS A NEGATIVE FREE ENERGY OF FORMATION AT 25*C, BELOW70,000 CALORIES PER GRAM ATOM OF OXYGEN WHICH COMPRISES PROVIDING APOWDER OF SAID MATRIX METAL OF MINUS 300 MICRONS IN SIZE HAVING ALLOYEDTHEREWITH UP TO ABOUT 5% BY WEIGHT OF A FRACTORY OXIDE-FORMING METALSELECTED FROM THE GROUP CONSISTING OF SI, MG. BE, ZR, TI, TH AND RAREEARTH METALS EACH OF WHOSE OXIDES IS SUBSTANTIALLY STABLE AT ELEVATEDTEMPERATURES AND IS CHARACTERIZED BY A NEGATIVE FREE ENERGY OF FORMATIONAT 25*C, OF OVER 90,000 CALORIES PER GRAM ATOM OF OXYGEN AND HAS AMELTING POINT OVER ABOUT 1500*C, SUBJECTING SAID POWDER TO OXIDATION BYHEATING IT AT AN ELEVATED TEMPERATURE AT LEAST ABOUT 500* C, BUT BELOWTHE MELTING POINT OF SAID MATRIX METAL IN AN OXIDIZING ATMOSPHERESUBJECTING SAID OXIDIZED POWDER TO ADDITIONAL HEATING IN AN INERTATMOSPHERE AT AN ELEVATED TEMPERATURE AT LEAST ABOUT 500*C, TO DECOMPOSEMATRIX METAL SURFACE OXIDE AND PROVIDE ADDISTIONAL OXYGEN FOR DIFFUSIONINTO THE POWDER TO CONVERT FURTHER REFRACTORY OXIDE-FORMING METAL INTODISPERSE OXIDE PHASE, HEATING SAID TREATED POWDER TO AN ELEVATEDTEMPERATURE BELOW THE MELTING POINT OF THE METAL POWDER IN A REDUCINGATMOSPHERE TO REDUCE EXCESS MATRIX METAL OXIDE REMAINING ON THE SURFACEOF THE POWDER, CONSOLIDATING SAID REDUCED POWDER TO A SUBSTANTIALLYSOLID COMPACT AND HOT EXTRUDING SAID COMPACT TO A DESIRED SHAPE, WHEREBYSAID SHAPE IS CHARACTERIZED BY A UNIFORM DISPERSION THROUGHOUT OF FINEPARTICLES OF A HARD REFRACTORY OXIDE.